BlockSite - BlockSite is an extension, which automagically blocks websites of your choice.
Freedom.to - Freedom is a productivity hack that lets you block apps, websites or the entire Internet on iPhones, iPads, Windows and Mac computers.
FocusMe - With so much access to information and distractions on the internet, it's easy to get sidetracked.
Stay Focused - More suitable with Google Chrome, this service enables you ensure you do not waste precious time on updating Facebook status or chatting with people.
Serene - The macOS app to get your focus back
GateSentry - A freeware web filtering application with HTTP/S filtering and time controls for all platforms...